Preparation of alloy steels



Patented June 27, 1933 um'reo STATES PATEN OFFICE HENRY C. IBIGGE, OF BETHLEHEM, PENNSYLVANIA, ASSIGNOR T0 BETHLEHEM STEEL COMPANY, A CORPORATION OF PENNSYLVANIA PREPARATION OF ALLOY STEELS No Drawing.

My invention relates to the preparation of alloy steels, more especially steels containing substantial amounts of chromium. More particularly my invention is directed to a process for alloy steel preparation in which zirconium or silicon-zirconium is added to the slag during the steel preparation.

My invention comprises the addition of z1rconium or zirconium alloys to the slag layer on a. bath of alloy steel to produce certain definite results both upon the metal bath and upon the slag to which the zirconium or alloy thereof is added.

By means of my invention less alloying constituent is lost than in the ordinary processes of preparing alloy steel.

Furthermore I obtain alloy steels which are relatively free from certain deleterious ingredients such as excessive amounts ofsulphur, phosphorus and oxygen. Moreover the steel prepared in accordance with my invention is non-raising in the mold, that is when the steel is poured into the mold it does not froth or rise.

The invention can probably be best presented by first setting forth a specific example thereof. Low carbon scrap is charged in a basic lined electric arc furnace. Limestone is added and the charge melted in the ordinary way. Iron ore is added in suflicient amount to eiiect the desired oxidation of the carbon content. The slag which has served its due refining influence is run. off and lime carbon is added in suflicient amount to form a further refining slag.

In the next stage of the operation the chrothe additions of installments'o-f low ferro chromium. Alternately to the additions of this ferro chromium to the metal bath, installments of an alloy of silicon and zirconium are added to the slag.

I proceed as follows: To the molten slag is added the silicon zirconium alloy, containing of zirconium and 57% of silicon. Shortly after the addition of the silicon-zirconium alloy low carbon ferro chromium is added to the metal bath and then another installment of silicon-zirconium alloy, then another-installment of ferro chromium, and so Application filed Jul 2, 1931. Serial No. 548,471.

on until the desired chromium content is secured in the steel. These alternate additions of ferro chromium to the steel bath and zirconium-silicon alloy to the slag are contlnued, in this particular case, until about 2400 lbs. of low carbon ferro chromium has been used, to give a steel containing about 1 2% of chromium. Each installment of the zirconium and silicon alloy is in an amount of from 20 to 60 lbs., 20 lbs. usually being satisfactory. When the desired chromium content of the composition has been attained the alloy is tapped.

In carrying out this operation I find it is frequently advantageous to add an installment of silicon-zirconium alloy shortly before tapping.

By this operation I lose much less chromium in the slag than occurs with the ordinary process for making chromium steels. In other words, a much greater percentage of the chromium goes into the metal and becomes aconstituent of the finished steel than is true of the usual practice.

Likewise in this process there is a much greater reduction of iron oxide and there is much less oxidation of the iron in the steel. As a result of the very effective reduction of the oxides of such metals as iron and chromium the slag obtained as a result of my operation is light in color and may properly be designated a White disintegrating slag.

The metal is very low in impurities, such as sulphur, and is relatively free from inclusions of all sorts. Upon the pouring of chromium alloy in the molds it is free from any tendency to rise, being radically difl'erent in this respect from most high chromium low carbon steels.

While in the example above given the slag treating alloy employed consists of zirconium very effectively. However I find that the most satisfactory results are obtained by the joint action ofthe zirconium and silicon, particularly as regards economy, less zircomum being required when associated with silicon than when the zirconium is used in the absence of another reducing agent.

Obviously the above example given is not intended to be restrictive as regards the alloy steels to be produced. .The process is very effective in the preparation of all high chromium steels, whether or not other constituents are present. It has been found to be very effective, for example, in the preparation of high chromium nickel steels, an example being the well known steels containing, say 18% chromium and 8% nickel.

The process is not limited to the preparation of chromium steels but is likewise advanpageous in the preparation of other alloy stee s.

Obviously my process is not to be limited to the carrying out of the operation in any particular type of furnace. While, in the illustration above given, an electric arc furnace is used, it is clear that other types of electric furnaces may be used. In fact, any type of furnace may be employed, whether electric or otherwise, that may be used in the preparation of alloy steels.

I appreciate the fact that it is not new to employ zirconium as a scavenging agent in the treatment and preparation of metal alloys. It is old, for example, to add zirconium or its alloys to the metal bath in such cases, but it is impossible by such procedure to obtain all the results which I obtain by adding it to the slag. 1

I also appreciate the fact that it is old to add deoxidizing elements such as silicon,

manganese, and aluminum and various combinat ons thereof to slag in the preparation of alloy steels. Such old practice, however, does not enable one to obtain the combination of results which I have set forth.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

1. In a process for the preparationof chromium containing steels, the step of adding zirconium to a slag on the molten bath of chromium containing steel.

2. In a process for the preparation of chromium containing steels, the step of adding a zirconium-silicon alloy to a slag upon a molten bath of chromium containing steel. I 3. In a process for the preparation of chromium containing steels, the steps of adding chromium to the metal bath at intervals and adding zirconium to the slag at intervals.

4. In a process for the preparation of chromium containing steels, the steps of alternately adding chromium to the metal bath and zirconium to the slag.

5. In a process for the preparation of chromium containing steels, the steps of alternately adding chromium to the metal bath and zirconium-silicon alloy to'the slag.

6. In a process for the preparation of chromium containing steels, the steps of preparing a ferrous bath, slagging o forming a highly basic slag upon the ferrous bath, adding chromium to the bath and adding zirconium to the slag.

7. In a process for the preparation of chromium containing steels, the she s of preparing a ferrous bath, slagging 0E, forming a highly basic slag upon the ferrous bath, adding an alloy containing silicon and zirconium to the slag.

8. In a process for the preparation of alloy steels, the step of adding zirconium to a slag on a molten bath of alloy steel.

In testimony whereof I hereunto afiix my signature.

HENRY C. BIGGE. 

